Life in the Clouds

I’ve spent many years extolling the virtues of life on a cold brown dwarf moon. Similar to the Galilean moons of Jupiter, a moon orbiting a sub-brown dwarf would be warmed internally by the tidal forces generated by its proximity to such a powerful gravitational force. Additionally, the sub-brown dwarf itself might provide some local heating, or at least an abundance of charged-particle strewn local magnetic fields to energise the sub-stellar environment. So, a habitable environment on a moon seems a likely scenario. If a cold, dark sub-brown dwarf were to be found orbiting the Sun at a great distance, then it neatly provides the grounding for extraterrestrial life on our doorstep (1).

This seems to me to be the simplest scenario for life in a sub-brown dwarf system. There are complexities – tidally-locked moons (2), lack of light, and so on. But the basics are there.

Another exotic possibility is that the sub-brown dwarf itself might harbour life. The complex cloud systems in these failed stars can contain layers which are at room temperature, and abundant in water and other chemical goodies which could form the building blocks of life. A team of astronomers from Edinburgh University have been considering this very point, wondering whether very simple life might be able to get going in the clouds of a cold brown dwarf (3). This life might arise in two ways – either somehow evolving from scratch in the cloud environment, or originally being seeded into it by an impacting asteroid or comet. Either way, conditions for life might be good, except for the lack of a solid surface to dwell on:

“Floating out by themselves in the Milky Way galaxy are perhaps a billion cold brown dwarfs, objects many times as massive as Jupiter but not big enough to ignite as a star. According to a new study, layers of their upper atmospheres sit at temperatures and pressures resembling those on Earth, and could host microbes that surf on thermal updrafts...Observations of cold brown dwarf atmospheres reveal most of the ingredients Earth life depends on: carbon, hydrogen, nitrogen, and oxygen, though perhaps not phosphorous.“ (4)

These ideas build upon work done by the late, great Carl Sagan (with his Cornell colleague E. E. Salpeter) on the potential for life in the clouds of the gas giant Jupiter, first considered back in the 1970s (5). They envisioned giant ‘floaters’ filled with hydrogen bobbing through the Jovian atmosphere, tiny ‘sinkers’ and self-propelled ‘hunters’ which had evolved from the lazy floaters (6). All very speculative, but presented in Dr Sagan’s inimitably compelling fashion.

By the way, anyone who thinks Sagan’s general skepticism outweighed his belief in the prevalence of life throughout the cosmos should read Donald Zygutis’s expose of Sagan’s long-held belief in ancient visits by aliens to Earth (7). Sagan thought that life, including technologically-savvy life, must be out there in abundance.

Over the lifespan of the galaxy, many interstellar-faring civilisations must have emerged, Sagan argued, based upon the statistical probabilities emerging from the Drake Equation (the odds seem way better these days (8)). Based upon a straightforward logical extrapolation, Sagan advocated that NASA, and other interested organisations, conduct an in-depth study of ancient myth to trace early contact with alien visitors. He even proposed that these might have included the Mesopotamian mythological creatures, the Apkallu:

“There are other legends which more nearly satisfy the foregoing contact criteria, and which deserve serious study in the present context. As one example, we may mention the Babylonian account of the origin of Sumerian civilisation by the Apkallu, representatives of an advanced, nonhuman and possibly extraterrestrial society” (9)

As another aside, Sagan’s SETI colleague Jill Tartar was the astronomer who first coined the term ‘brown dwarf’ back in 1975 (10). The colour nomenclature chosen for these objects was an educated guess at the time. Brown dwarfs are red, cooling in tone to magentas and purples as they move into the smaller, older and colder categories of sub-stellar objects.

Now, Jupiter’s cloud systems are quite a bit colder than those of its more massive sub-brown dwarf cousins. So, if Sagan thought life could possibly exist in the frigid gaseous environments of our solar system’s most massive planet, then the potential for life in the atmosphere of a cold brown dwarf would have got a big thumbs-up from him, I think. However, brown dwarf expert Mark Marley expressed a sceptical note about this Scottish research on Twitter:

“This is a cute idea but I really don’t think brown dwarfs are habitable. Way too much vertical mixing.” (11)

Dr Marley may be right, of course. This is all very speculative. Certainly, the Scottish team have downgraded expectations considerably from the ideas ‘floated about’ in the halcyon days of ‘Cosmos’. From Sagan’s original grand vision of enormous floating organic bags of gas back then, to mere microbial forms these days. This reflects a more conservative view of what we might expect to find ‘out there’ prevalent in science now. Less little green men (or organic helium balloons in this case), more extremeophiles eking out living in the nooks and crannies of barren alien worlds. It’s sad, really.

For me, though, this is all rather academic. Because the real prize is what’s going on in the planetary systems of these cold brown dwarfs. In my opinion, quite a bit!